1. Field of the Invention
The present invention relates to a process for coating a cylindrical or columnar base with a fluororesin, a toner-fixing member produced by this process, and an electrophotographic apparatus equipped with the toner-fixing member, such as a copying machine or LBP.
2. Related Background Art
A fixing roller, fixing film, pressure roller and the like used as fixing members in electrophotographic image-forming apparatus are required to have good toner-parting or releasing property from the viewpoint of their use, and a fluororesin is often used for their surface layers.
When a full-color toner image is formed, a fixing roller or fixing film for fixing toner layers of 4 layers at the maximum must have such flexibility as can follow irregularities of toners and a transfer medium in order that a fluororesin layer, which is a toner-parting surface layer, completely transfers heat to the toners to provide good fixing ability of the toners to the transfer medium. Therefore, a fixing member having a construction such that a flexible elastic layer is provided under the fluororesin layer, or the toner-parting layer is used.
A fixing member obtained by forming an elastic layer on a cylindrical or columnar metal mandrel and forming a film of a fluororesin as a toner-parting layer around the peripheral surface of the elastic layer has often been used as a fixing member for an electrophotographic image-forming apparatus. Recently, a fixing member obtained by forming an elastic layer on a core made of a heat-resisting resin and forming a film of a fluororesin as a toner-parting layer around the peripheral surface of the elastic layer has also been used.
As a process for coating a peripheral wall of a cylindrical or columnar base with a fluororesin, a process in which powder or a dispersion of the fluororesin is applied onto the base and then heated and calcined has been used. When the fluororesin is heated and calcined, it heats the fluororesin up to at least the melting point thereof so as to calcine it into a film.
However, the fluororesin-coating process like the conventional process involves the following problems.
First of all, in the case where the base is an elastic body, a fluororesin is applied onto the elastic body and heated and calcined, the smoothness of a fluororesin layer formed into a film is lowered because of the extremely high melt viscosity of the fluororesin even when the fluororesin is heated and calcined at a considerably higher temperature than the melting point of the fluororesin. When such fluororesin-calcining conditions as described above are practiced, the elastic body is damaged to an extremely great extent because there is no elastic body which can withstand such a high temperature. As a result, the compression set of the elastic layer deteriorates, resulting in a failure to attain the good paper-feeding property required of fixing members. When the calcining temperature of the fluororesin is lowered in order to reduce such damage, the fluororesin is not quite melted which causes problems that the surface of the fluororesin layer cracks, and the desired surface profile cannot be achieved.
In order to solve the above problems, the present inventors have proposed a process of heating, calcining and forming a fluororesin into a layer while pressing the fluororesin layer between the elastic body and a face transfer member arranged outside the fluororesin layer to transfer the surface pattern of the face transfer member to the surface of the fluororesin. As a result, it became possible to form the fluororesin into a film at a temperature lower than usual while controlling the surface pattern of the fluororesin, and so it followed that the damage of the underlying elastic body (rubber) could be reduced to a comparatively small extent. However, even this process was unable to completely prevent damage to elastic body (rubber).